Question: Which of these numbers is composite? ${5,\ 41,\ 47,\ 55,\ 71}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 5, 41, 47, and 71 each have only two factors. The factors of 55 are 1, 5, 11, and 55. Thus, 55 is the composite number.